U.S. patent number 7,688,494 [Application Number 12/115,395] was granted by the patent office on 2010-03-30 for electrode and interconnect materials for mems devices.
This patent grant is currently assigned to QUALCOMM MEMS Technologies, Inc.. Invention is credited to Evgeni Gousev, Gang Xu.
United States Patent |
7,688,494 |
Xu , et al. |
March 30, 2010 |
Electrode and interconnect materials for MEMS devices
Abstract
A microelectromechanical (MEMS) device is presented which
comprises a metallized semiconductor. The metallized semiconductor
can be used for conductor applications because of its low
resistivity, and for transistor applications because of its
semiconductor properties. In addition, the metallized semiconductor
can be tuned to have optical properties which allow it to be useful
for optical MEMS devices.
Inventors: |
Xu; Gang (Cupertino, CA),
Gousev; Evgeni (Saratoga, CA) |
Assignee: |
QUALCOMM MEMS Technologies,
Inc. (San Diego, CA)
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Family
ID: |
38660920 |
Appl.
No.: |
12/115,395 |
Filed: |
May 5, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080239449 A1 |
Oct 2, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11416920 |
May 3, 2006 |
7369292 |
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Current U.S.
Class: |
359/245;
359/290 |
Current CPC
Class: |
B81C
1/00246 (20130101); G02B 26/001 (20130101); B81B
2201/047 (20130101) |
Current International
Class: |
G02F
1/03 (20060101); G02B 26/00 (20060101) |
Field of
Search: |
;359/245,290 |
References Cited
[Referenced By]
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Primary Examiner: Schwartz; Jordan M.
Assistant Examiner: Jones; James C
Attorney, Agent or Firm: Knobbe, Martens, Olson & Bear
LLP
Parent Case Text
RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No.
11/416,920, titled "Electrode and Interconnect Materials for MEMS
Devices," filed May 3, 2006, the specification of which is hereby
incorporated by reference, in its entirety.
Claims
What is claimed is:
1. A microelectromechanical system (MEMS) device, comprising: a
conductor comprising a metallized semiconductor layer; and a
movable element configured to be actuated by the conductor, wherein
the metallized semiconductor layer is partially reflective,
electrically conductive, and configured to transmit light towards
the movable element.
2. The device of claim 1, wherein the metallized semiconductor
layer comprises at least one of silicon, germanium and gallium
arsenide.
3. The device of claim 1, wherein the metalized semiconductor layer
comprises at least one of nickel, molybdenum, cobalt, tantalum, and
titanium.
4. The device of claim 1, further comprising electronic circuitry
configured to actuate the movable element, wherein the electronic
circuitry comprises a semiconductor.
5. The device of claim 1, wherein the conductor comprises an
electrode, and the movable element moves in response to an
electrical potential between the conductor and the movable
element.
6. The device of claim 1, further comprising an interferometric
light modulation cavity between the movable element and the
conductor.
7. The device of claim 1, wherein the electrode has an electrical
resistivity from about 10 .mu..OMEGA.cm to about 100
.mu..OMEGA.cm.
8. The device of claim 7, wherein the electrode has a thickness
from about 5 nm to about 100 nm.
9. The device of claim 1, further comprising: a display; a
processor configured to communicate with the display, the processor
configured to process image data; and a memory device configured to
communicate with the processor.
10. The device of claim 9, further comprising a driver circuit
configured to send at least one signal to the display.
11. The device of claim 10, further comprising a controller
configured to send at least a portion of the image data to the
driver circuit.
12. The device as recited in claim 9, further comprising an image
source module configured to send the image data to the
processor.
13. The device of claim 12, wherein the image source module
comprises at least one of a receiver, transceiver, and
transmitter.
14. The device as recited in claim 9, further comprising an input
device configured to receive input data and to communicate the
input data to the processor.
15. A method of using a microelectromechanical system (MEMS)
device, comprising: applying a voltage to a conductor comprising a
metallized semiconductor layer, wherein a movable element is
actuated in response to the voltage; and partially transmitting
light, partially reflecting light, and conducting electricity with
the metallized semiconductor layer.
16. The method of claim 15, further comprising applying a voltage
to electronic circuitry to actuate the movable element, wherein the
electronic circuitry comprises a semiconductor.
17. The method of claim 15, further comprising interferometrically
modulating light based at least in part on an electrical potential
between the conductor and the movable element.
18. A method of manufacturing a microelectromechanical system
(MEMS) device, the method comprising: forming a conductor
comprising a metallized semiconductor layer; and forming a movable
element configured to be actuated by the conductor, wherein the
metallized semiconductor layer is partially reflective,
electrically conductive, and configured to transmit light towards
the movable element.
19. The method of claim 18, wherein forming the conductor is
performed on a first production line configured to produce thin
film transistors.
20. The method of claim 18, further comprising electrically
connecting the conductor to electronic circuitry configured to
actuate the movable element, wherein the electronic circuitry
comprises a semiconductor.
21. The method of claim 18, further comprising forming an
interferometric light modulation cavity between the movable element
and the conductor.
22. The device of claim 1, wherein the metallized semiconductor
layer comprises at least one of a metal silicide, a metal
germanide, a metal germosilicide, NiSi, CoSi.sub.2, MoSi, CoSi,
TaSi, TiSi, and Ni(Si.sub.x-1Ge.sub.x).
23. The method of claim 15, wherein the metallized semiconductor
layer comprises at least one of a metal silicide, a metal
germanide, a metal germosilicide, NiSi, CoSi.sub.2, MoSi, CoSi,
TaSi, TiSi, and Ni(Si.sub.x-1Ge.sub.x).
24. The method of claim 18, wherein the metallized semiconductor
layer comprises at least one of a metal silicide, a metal
germanide, a metal germosilicide, NiSi, CoSi.sub.2, MoSi, CoSi,
TaSi, TiSi, and Ni(Si.sub.x-1Ge.sub.x).
Description
BACKGROUND
1. Field of the Invention
The field of the invention relates to microelectromechanical
systems (MEMS). More specifically, the invention relates to MEMS
devices having an electrical contact, electrode interconnect
structures. One particular application can be found in capacitive
MEMS devices. Finally, due to the (semi)-transparent nature of the
electrode material in visible light, the invention also relates to
optical MEMS devices, in general, and interferometric light
modulators in particular.
2. Description of the Related Technology
Microelectromechanical systems (MEMS) include micro mechanical
elements, actuators, and electronics. Micromechanical elements may
be created using deposition, etching, and or other micromachining
processes that etch away parts of substrates and/or deposited
material layers or that add layers to form electrical and
electromechanical devices. One type of MEMS device is called an
interferometric modulator. As used herein, the term interferometric
modulator or interferometric light modulator refers to a device
that selectively absorbs and/or reflects light using the principles
of optical interference. In certain embodiments, an interferometric
modulator may have a pair of conductive plates, one or both of
which may be transparent and/or reflective in whole or part and
capable of relative motion upon application of an appropriate
electrical signal. In this type of device, one plate may be a
stationary layer deposited on a substrate and the other plate may
be a metallic membrane separated from the stationary layer by an
air gap. The position of one plate in relation to another can
change the optical interference of light incident on the
interferometric modulator. Such devices have a wide range of
applications, and it would be beneficial in the art to utilize
and/or modify the characteristics of these types of devices so that
their features can be exploited in improving existing products and
creating new products that have not yet been developed.
SUMMARY OF CERTAIN EMBODIMENTS
The system, method, and devices of the invention each have several
aspects, no single one of which is solely responsible for its
desirable attributes. Without limiting the scope of this invention,
its more prominent features will now be discussed briefly. After
considering this discussion, and particularly after reading the
section entitled "Detailed Description of Certain Embodiments" one
will understand how the features of this invention provide
advantages over other display devices.
One embodiment is a microelectromechanical system (MEMS) device,
including a conducting electrode including a metallized
semiconductor, and a movable element configured to be actuated by
the conductor.
Another embodiment is a method of using a microelectromechanical
system (MEMS) device, including applying a voltage to a conductor
including a metallized semiconductor, where a movable element is
actuated in response to the voltage.
Another embodiment is a method of manufacturing a
microelectromechanical system (MEMS) device, the method including
forming a conductor including a metallized semiconductor, and
forming a movable element configured to be actuated by the
conductor.
Another embodiment is a microelectromechanical system (MEMS)
device, including means for actuating a MEMS element, where the
actuating means is configured to partially transmit light and to
partially reflect light.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view depicting a portion of one embodiment
of an interferometric modulator display in which a movable
reflective layer of a first interferometric modulator is in a
relaxed position and a movable reflective layer of a second
interferometric modulator is in an actuated position.
FIG. 2 is a system block diagram illustrating one embodiment of an
electronic device incorporating a 3.times.3 interferometric
modulator display.
FIG. 3 is a diagram of movable mirror position versus applied
voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
FIG. 4 is an illustration of a set of row and column voltages that
may be used to drive an interferometric modulator display.
FIGS. 5A and 5B illustrate one exemplary timing diagram for row and
column signals that may be used to write a frame of display data to
the 3.times.3 interferometric modulator display of FIG. 2.
FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a visual display device comprising a plurality of
interferometric modulators.
FIG. 7A is a cross section of the device of FIG. 1.
FIG. 7B is a cross section of an alternative embodiment of an
interferometric modulator.
FIG. 7C is a cross section of another alternative embodiment of an
interferometric modulator.
FIG. 7D is a cross section of yet another alternative embodiment of
an interferometric modulator.
FIG. 7E is a cross section of an additional alternative embodiment
of an interferometric modulator.
FIGS. 8A and 8B are cross-sections of an embodiment of a MEMS
device with metal silicide, metal germanide, or metal
germosilicide.
FIGS. 9A to 9D are cross-sections of the MEMS device shown in FIGS.
8A and 8B at various stages in a manufacturing process.
FIG. 10 is a cross-section of an interferometric modulator with an
electrode comprising metal silicide, metal germanide, or metal
germosilicide.
FIGS. 11A to 11C are cross-sections of the interferometric
modulator of FIG. 10 and a transistor at various stages in a
manufacturing process.
FIGS. 12A and 12B are graphs showing the reflectance of simulated
interferometric modulators across wavelengths of visible light.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
The following detailed description is directed to certain specific
embodiments of the invention. However, the invention can be
embodied in a multitude of different ways. In this description,
reference is made to the drawings wherein like parts are designated
with like numerals throughout. As will be apparent from the
following description, the embodiments may be implemented in any
device that is configured to display an image, whether in motion
(e.g., video) or stationary (e.g., still image), and whether
textual or pictorial. More particularly, it is contemplated that
the embodiments may be implemented in or associated with a variety
of electronic devices such as, but not limited to, mobile
telephones, wireless devices, personal data assistants (PDAs),
hand-held or portable computers, GPS receivers/navigators, cameras,
MP3 players, camcorders, game consoles, wrist watches, clocks,
calculators, television monitors, flat panel displays, computer
monitors, auto displays (e.g., odometer display, etc.), cockpit
controls and/or displays, display of camera views (e.g., display of
a rear view camera in a vehicle), electronic photographs,
electronic billboards or signs, projectors, architectural
structures, packaging, and aesthetic structures (e.g., display of
images on a piece of jewelry). MEMS devices of similar structure to
those described herein can also be used in non-display applications
such as in electronic switching devices.
Embodiments of the invention relate to MEMS devices that include a
conductor made of a metallized semiconductor material. In one
embodiment, the MEMS device is an interferometric modulator with a
transparent substrate, an electrode conductor and a movable mirror.
Creating an electrical potential between the movable mirror and the
electrode conductor results in movement of the movable mirror
towards the electrode conductor. In one embodiment, the electrode
conductor comprises a metallized semiconductor, such as a metal
silicide, metal germanide or metal germosilicide. By using such
materials, the absorber layer and conductor layer in a typical
interferometric modulator can be combined into a single layer.
One interferometric modulator display embodiment comprising an
interferometric MEMS display element is illustrated in FIG. 1. In
these devices, the pixels are in either a bright or dark state. In
the bright ("on" or "open") state, the display element reflects a
large portion of incident visible light to a user. When in the dark
("off" or "closed") state, the display element reflects little
incident visible light to the user. Depending on the embodiment,
the light reflectance properties of the "on" and "off" states may
be reversed. MEMS pixels can be configured to reflect predominantly
at selected colors, allowing for a color display in addition to
black and white.
FIG. 1 is an isometric view depicting two adjacent pixels in a
series of pixels of a visual display, wherein each pixel comprises
a MEMS interferometric modulator. In some embodiments, an
interferometric modulator display comprises a row/column array of
these interferometric modulators. Each interferometric modulator
includes a pair of reflective layers positioned at a variable and
controllable distance from each other to form a resonant optical
cavity with at least one variable dimension. In one embodiment, one
of the reflective layers may be moved between two positions. In the
first position, referred to herein as the relaxed position, the
movable reflective layer is positioned at a relatively large
distance from a fixed partially reflective layer. In the second
position, referred to herein as the actuated position, the movable
reflective layer is positioned more closely adjacent to the
partially reflective layer. Incident light that reflects from the
two layers interferes constructively or destructively depending on
the position of the movable reflective layer, producing either an
overall reflective or non-reflective state for each pixel.
The depicted portion of the pixel array in FIG. 1 includes two
adjacent interferometric modulators 12a and 12b. In the
interferometric modulator 12a on the left, a movable reflective
layer 14a is illustrated in a relaxed position at a predetermined
distance from an optical stack 16a, which includes a partially
reflective layer. In the interferometric modulator 12b on the
right, the movable reflective layer 14b is illustrated in an
actuated position adjacent to the optical stack 16b.
The optical stacks 16a and 16b (collectively referred to as optical
stack 16), as referenced herein, typically comprise of several
fused layers, which can include an electrode layer, such as indium
tin oxide (ITO), a partially reflective layer, such as chromium,
and a transparent dielectric. The optical stack 16 is thus
electrically conductive, partially transparent and partially
reflective, and may be fabricated, for example, by depositing one
or more of the above layers onto a transparent substrate 20. The
partially reflective layer can be formed from a variety of
materials that are partially reflective such as various metals,
semiconductors, and dielectrics. Some examples of suitable
materials include oxides, nitrides, and fluorides. Other examples
include germanium (Ge), nickel silicide (NiSi), molybdenum (Mo),
titanium (Ti), tantalum (Ta), and platinum (Pt). The partially
reflective layer can be formed of one or more layers of materials,
and each of the layers can be formed of a single material or a
combination of materials.
In some embodiments, the layers of the optical stack are patterned
into parallel strips, and may form row electrodes in a display
device as described further below. The movable reflective layers
14a, 14b may be formed as a series of parallel strips of a
deposited metal layer or layers (orthogonal to the row electrodes
of 16a, 16b) deposited on top of posts 18 and an intervening
sacrificial material deposited between the posts 18. When the
sacrificial material is etched away, the movable reflective layers
14a, 14b are separated from the optical stacks 16a, 16b by a
defined gap 19. A highly conductive and reflective material such as
aluminum may be used for the reflective layers 14, and these strips
may form column electrodes in a display device.
With no applied voltage, the cavity 19 remains between the movable
reflective layer 14a and optical stack 16a, with the movable
reflective layer 14a in a mechanically relaxed state, as
illustrated by the pixel 12a in FIG. 1. However, when a potential
difference is applied to a selected row and column, the capacitor
formed at the intersection of the row and column electrodes at the
corresponding pixel becomes charged, and electrostatic forces pull
the electrodes together. If the voltage is high enough, the movable
reflective layer 14 is deformed and is forced against the optical
stack 16. A dielectric layer (not illustrated in this Figure)
within the optical stack 16 may prevent shorting and control the
separation distance between layers 14 and 16, as illustrated by
pixel 12b on the right in FIG. 1. The behavior is the same
regardless of the polarity of the applied potential difference. In
this way, row/column actuation that can control the reflective vs.
non-reflective pixel states is analogous in many ways to that used
in conventional LCD and other display technologies.
FIGS. 2 through 5 illustrate one exemplary process and system for
using an array of interferometric modulators in a display
application.
FIG. 2 is a system block diagram illustrating one embodiment of an
electronic device that may incorporate aspects of the invention. In
the exemplary embodiment, the electronic device includes a
processor 21 which may be any general purpose single- or multi-chip
microprocessor such as an ARM, Pentium.RTM., Pentium II.RTM.,
Pentium III.RTM., Pentium IV.RTM., Pentium.RTM. Pro, an 8051, a
MIPS.RTM., a Power PC.RTM., an ALPHA.RTM., or any special purpose
microprocessor such as a digital signal processor, microcontroller,
or a programmable gate array. As is conventional in the art, the
processor 21 may be configured to execute one or more software
modules. In addition to executing an operating system, the
processor may be configured to execute one or more software
applications, including a web browser, a telephone application, an
email program, or any other software application.
In one embodiment, the processor 21 is also configured to
communicate with an array driver 22. In one embodiment, the array
driver 22 includes a row driver circuit 24 and a column driver
circuit 26 that provide signals to a display array or panel 30. The
cross section of the array illustrated in FIG. 1 is shown by the
lines 1-1 in FIG. 2. For MEMS interferometric modulators, the
row/column actuation protocol may take advantage of a hysteresis
property of these devices illustrated in FIG. 3. It may require,
for example, a 10 volt potential difference to cause a movable
layer to deform from the relaxed state to the actuated state.
However, when the voltage is reduced from that value, the movable
layer maintains its state as the voltage drops back below 10 volts.
In the exemplary embodiment of FIG. 3, the movable layer does not
relax completely until the voltage drops below 2 volts. There is
thus a range of voltage, about 3 to 7 V in the example illustrated
in FIG. 3, where there exists a window of applied voltage within
which the device is stable in either the relaxed or actuated state.
This is referred to herein as the "hysteresis window" or "stability
window." For a display array having the hysteresis characteristics
of FIG. 3, the row/column actuation protocol can be designed such
that during row strobing, pixels in the strobed row that are to be
actuated are exposed to a voltage difference of about 10 volts, and
pixels that are to be relaxed are exposed to a voltage difference
of close to zero volts. After the strobe, the pixels are exposed to
a steady state voltage difference of about 5 volts such that they
remain in whatever state the row strobe put them in. After being
written, each pixel sees a potential difference within the
"stability window" of 3-7 volts in this example. This feature makes
the pixel design illustrated in FIG. 1 stable under the same
applied voltage conditions in either an actuated or relaxed
pre-existing state. Since each pixel of the interferometric
modulator, whether in the actuated or relaxed state, is essentially
a capacitor formed by the fixed and moving reflective layers, this
stable state can be held at a voltage within the hysteresis window
with almost no power dissipation. Essentially no current flows into
the pixel if the applied potential is fixed.
In typical applications, a display frame may be created by
asserting the set of column electrodes in accordance with the
desired set of actuated pixels in the first row. A row pulse is
then applied to the row 1 electrode, actuating the pixels
corresponding to the asserted column lines. The asserted set of
column electrodes is then changed to correspond to the desired set
of actuated pixels in the second row. A pulse is then applied to
the row 2 electrode, actuating the appropriate pixels in row 2 in
accordance with the asserted column electrodes. The row 1 pixels
are unaffected by the row 2 pulse, and remain in the state they
were set to during the row 1 pulse. This may be repeated for the
entire series of rows in a sequential fashion to produce the frame.
Generally, the frames are refreshed and/or updated with new display
data by continually repeating this process at some desired number
of frames per second. A wide variety of protocols for driving row
and column electrodes of pixel arrays to produce display frames are
also well known and may be used in conjunction with the present
invention.
FIGS. 4 and 5 illustrate one possible actuation protocol for
creating a display frame on the 3.times.3 array of FIG. 2. FIG. 4
illustrates a possible set of column and row voltage levels that
may be used for pixels exhibiting the hysteresis curves of FIG. 3.
In the FIG. 4 embodiment, actuating a pixel involves setting the
appropriate column to -V.sub.bias, and the appropriate row to
+.DELTA.V, which may correspond to -5 volts and +5 volts
respectively Relaxing the pixel is accomplished by setting the
appropriate column to +V.sub.bias, and the appropriate row to the
same +.DELTA.V, producing a zero volt potential difference across
the pixel. In those rows where the row voltage is held at zero
volts, the pixels are stable in whatever state they were originally
in, regardless of whether the column is at +V.sub.bias, or
-V.sub.bias. As is also illustrated in FIG. 4, it will be
appreciated that voltages of opposite polarity than those described
above can be used, e.g., actuating a pixel can involve setting the
appropriate column to +V.sub.bias, and the appropriate row to
-.DELTA.V. In this embodiment, releasing the pixel is accomplished
by setting the appropriate column to -V.sub.bias, and the
appropriate row to the same -.DELTA.V, producing a zero volt
potential difference across the pixel.
FIG. 5B is a timing diagram showing a series of row and column
signals applied to the 3.times.3 array of FIG. 2 which will result
in the display arrangement illustrated in FIG. 5A, where actuated
pixels are non-reflective. Prior to writing the frame illustrated
in FIG. 5A, the pixels can be in any state, and in this example,
all the rows are at 0 volts, and all the columns are at +5 volts.
With these applied voltages, all pixels are stable in their
existing actuated or relaxed states.
In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3)
are actuated. To accomplish this, during a "line time" for row 1,
columns 1 and 2 are set to -5 volts, and column 3 is set to +5
volts. This does not change the state of any pixels, because all
the pixels remain in the 3-7 volt stability window. Row 1 is then
strobed with a pulse that goes from 0, up to 5 volts, and back to
zero. This actuates the (1,1) and (1,2) pixels and relaxes the
(1,3) pixel. No other pixels in the array are affected. To set row
2 as desired, column 2 is set to -5 volts, and columns 1 and 3 are
set to +5 volts. The same strobe applied to row 2 will then actuate
pixel (2,2) and relax pixels (2,1) and (2,3). Again, no other
pixels of the array are affected. Row 3 is similarly set by setting
columns 2 and 3 to -5 volts, and column 1 to +5 volts. The row 3
strobe sets the row 3 pixels as shown in FIG. 5A. After writing the
frame, the row potentials are zero, and the column potentials can
remain at either +5 or -5 volts, and the display is then stable in
the arrangement of FIG. 5A. It will be appreciated that the same
procedure can be employed for arrays of dozens or hundreds of rows
and columns. It will also be appreciated that the timing, sequence,
and levels of voltages used to perform row and column actuation can
be varied widely within the general principles outlined above, and
the above example is exemplary only, and any actuation voltage
method can be used with the systems and methods described
herein.
FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a display device 40. The display device 40 can be,
for example, a cellular or mobile telephone. However, the same
components of display device 40 or slight variations thereof are
also illustrative of various types of display devices such as
televisions and portable media players.
The display device 40 includes a housing 41, a display 30, an
antenna 43, a speaker 44, an input device 48, and a microphone 46.
The housing 41 is generally formed from any of a variety of
manufacturing processes as are well known to those of skill in the
art, including injection molding, and vacuum forming. In addition,
the housing 41 may be made from any of a variety of materials,
including but not limited to plastic, metal, glass, rubber, and
ceramic, or a combination thereof. In one embodiment the housing 41
includes removable portions (not shown) that may be interchanged
with other removable portions of different color, or containing
different logos, pictures, or symbols.
The display 30 of exemplary display device 40 may be any of a
variety of displays, including a bi-stable display, as described
herein. In other embodiments, the display 30 includes a flat-panel
display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described
above, or a non-flat-panel display, such as a CRT or other tube
device, as is well known to those of skill in the art. However, for
purposes of describing the present embodiment, the display 30
includes an interferometric modulator display, as described
herein.
The components of one embodiment of exemplary display device 40 are
schematically illustrated in FIG. 6B. The illustrated exemplary
display device 40 includes a housing 41 and can include additional
components at least partially enclosed therein. For example, in one
embodiment, the exemplary display device 40 includes a network
interface 27 that includes an antenna 43 which is coupled to a
transceiver 47. The transceiver 47 is connected to a processor 21,
which is connected to conditioning hardware 52. The conditioning
hardware 52 may be configured to condition a signal (e.g. filter a
signal). The conditioning hardware 52 is connected to a speaker 45
and a microphone 46. The processor 21 is also connected to an input
device 48 and a driver controller 29. The driver controller 29 is
coupled to a frame buffer 28, and to an array driver 22, which in
turn is coupled to a display array 30. A power supply 50 provides
power to all components as required by the particular exemplary
display device 40 design.
The network interface 27 includes the antenna 43 and the
transceiver 47 so that the exemplary display device 40 can
communicate with one or more devices over a network. In one
embodiment the network interface 27 may also have some processing
capabilities to relieve requirements of the processor 21. The
antenna 43 is any antenna known to those of skill in the art for
transmitting and receiving signals. In one embodiment, the antenna
transmits and receives RF signals according to the IEEE 802.11
standard, including IEEE 802.11(a), (b), or (g). In another
embodiment, the antenna transmits and receives RF signals according
to the BLUETOOTH standard. In the case of a cellular telephone, the
antenna is designed to receive CDMA, GSM, AMPS or other known
signals that are used to communicate within a wireless cell phone
network. The transceiver 47 pre-processes the signals received from
the antenna 43 so that they may be received by and further
manipulated by the processor 21. The transceiver 47 also processes
signals received from the processor 21 so that they may be
transmitted from the exemplary display device 40 via the antenna
43.
In an alternative embodiment, the transceiver 47 can be replaced by
a receiver. In yet another alternative embodiment, network
interface 27 can be replaced by an image source, which can store or
generate image data to be sent to the processor 21. For example,
the image source can be a digital video disc (DVD) or a hard-disc
drive that contains image data, or a software module that generates
image data.
Processor 21 generally controls the overall operation of the
exemplary display device 40. The processor 21 receives data, such
as compressed image data from the network interface 27 or an image
source, and processes the data into raw image data or into a format
that is readily processed into raw image data. The processor 21
then sends the processed data to the driver controller 29 or to
frame buffer 28 for storage. Raw data typically refers to the
information that identifies the image characteristics at each
location within an image. For example, such image characteristics
can include color, saturation, and gray-scale level.
In one embodiment, the processor 21 includes a microcontroller,
CPU, or logic unit to control operation of the exemplary display
device 40. Conditioning hardware 52 generally includes amplifiers
and filters for transmitting signals to the speaker 45, and for
receiving signals from the microphone 46. Conditioning hardware 52
may be discrete components within the exemplary display device 40,
or may be incorporated within the processor 21 or other
components.
The driver controller 29 takes the raw image data generated by the
processor 21 either directly from the processor 21 or from the
frame buffer 28 and reformats the raw image data appropriately for
high speed transmission to the array driver 22. Specifically, the
driver controller 29 reformats the raw image data into a data flow
having a raster-like format, such that it has a time order suitable
for scanning across the display array 30. Then the driver
controller 29 sends the formatted information to the array driver
22. Although a driver controller 29, such as a LCD controller, is
often associated with the system processor 21 as a stand-alone
Integrated Circuit (IC), such controllers may be implemented in
many ways. They may be embedded in the processor 21 as hardware,
embedded in the processor 21 as software, or fully integrated in
hardware with the array driver 22.
Typically, the array driver 22 receives the formatted information
from the driver controller 29 and reformats the video data into a
parallel set of waveforms that are applied many times per second to
the hundreds and sometimes thousands of leads coming from the
display's x-y matrix of pixels.
In one embodiment, the driver controller 29, array driver 22, and
display array 30 are appropriate for any of the types of displays
described herein. For example, in one embodiment, driver controller
29 is a conventional display controller or a bi-stable display
controller (e.g., an interferometric modulator controller). In
another embodiment, array driver 22 is a conventional driver or a
bi-stable display driver (e.g., an interferometric modulator
display). In one embodiment, a driver controller 29 is integrated
with the array driver 22. Such an embodiment is common in highly
integrated systems such as cellular phones, watches, and other
small area displays. In yet another embodiment, display array 30 is
a typical display array or a bi-stable display array (e.g., a
display including an array of interferometric modulators).
The input device 48 allows a user to control the operation of the
exemplary display device 40. In one embodiment, input device 48
includes a keypad, such as a QWERTY keyboard or a telephone keypad,
a button, a switch, a touch-sensitive screen, a pressure- or
heat-sensitive membrane. In one embodiment, the microphone 46 is an
input device for the exemplary display device 40. When the
microphone 46 is used to input data to the device, voice commands
may be provided by a user for controlling operations of the
exemplary display device 40.
Power supply 50 can include a variety of energy storage devices as
are well known in the art. For example, in one embodiment, power
supply 50 is a rechargeable battery, such as a nickel-cadmium
battery or a lithium ion battery. In another embodiment, power
supply 50 is a renewable energy source, a capacitor, or a solar
cell, including a plastic solar cell, and solar-cell paint. In
another embodiment, power supply 50 is configured to receive power
from a wall outlet.
In some implementations control programmability resides, as
described above, in a driver controller which can be located in
several places in the electronic display system. In some cases
control programmability resides in the array driver 22. Those of
skill in the art will recognize that the above-described
optimization may be implemented in any number of hardware and/or
software components and in various configurations.
The details of the structure of interferometric modulators that
operate in accordance with the principles set forth above may vary
widely. For example, FIGS. 7A-7E illustrate five different
embodiments of the movable reflective layer 14 and its supporting
structures. FIG. 7A is a cross section of the embodiment of FIG. 1,
where a strip of metal material 14 is deposited on orthogonally
extending supports 18. In FIG. 7B, the moveable reflective layer 14
is attached to supports at the corners only, on tethers 32. In FIG.
7C, the moveable reflective layer 14 is suspended from a deformable
layer 34, which may comprise a flexible metal. The deformable layer
34 connects, directly or indirectly, to the substrate 20 around the
perimeter of the deformable layer 34. These connections are herein
referred to as support posts. The embodiment illustrated in FIG. 7D
has support post plugs 42 upon which the deformable layer 34 rests.
The movable reflective layer 14 remains suspended over the cavity,
as in FIGS. 7A-7C, but the deformable layer 34 does not form the
support posts by filling holes between the deformable layer 34 and
the optical stack 16. Rather, the support posts are formed of a
planarization material, which is used to form support post plugs
42. The embodiment illustrated in FIG. 7E is based on the
embodiment shown in FIG. 7D, but may also be adapted to work with
any of the embodiments illustrated in FIGS. 7A-7C as well as
additional embodiments not shown. In the embodiment shown in FIG.
7E, an extra layer of metal or other conductive material has been
used to form a bus structure 44. This allows signal routing along
the back of the interferometric modulators, eliminating a number of
electrodes that may otherwise have had to be formed on the
substrate 20.
In embodiments such as those shown in FIG. 7, the interferometric
modulators function as direct-view devices, in which images are
viewed from the front side of the transparent substrate 20, the
side opposite to that upon which the modulator is arranged. In
these embodiments, the reflective layer 14 optically shields the
portions of the interferometric modulator on the side of the
reflective layer opposite the substrate 20, including the
deformable layer 34. This allows the shielded areas to be
configured and operated upon without negatively affecting the image
quality. Such shielding allows the bus structure 44 in FIG. 7E,
which provides the ability to separate the optical properties of
the modulator from the electromechanical properties of the
modulator, such as addressing and the movements that result from
that addressing. This separable modulator architecture allows the
structural design and materials used for the electromechanical
aspects and the optical aspects of the modulator to be selected and
to function independently of each other. Moreover, the embodiments
shown in FIGS. 7C-7E have additional benefits deriving from the
decoupling of the optical properties of the reflective layer 14
from its mechanical properties, which are carried out by the
deformable layer 34. This allows the structural design and
materials used for the reflective layer 14 to be optimized with
respect to the optical properties, and the structural design and
materials used for the deformable layer 34 to be optimized with
respect to desired mechanical properties.
FIGS. 8A and 8B show MEMS element 818 which operates as a switch.
MEMS element 818 comprises insulator 808, which is formed on
substrate 820 and supports a portion of mechanical layer 814.
Electrode 812 is formed on substrate 820 so as to be spaced apart
from mechanical layer 814 and is positioned between substrate 820
and mechanical layer 814 near a portion of mechanical layer 814 not
supported by insulator 808. MEMS element 818 also comprises
terminal 810 formed on the substrate so as to be positioned between
substrate 820 and mechanical layer 814 near the unsupported end of
mechanical layer 814.
Operation of the MEMS element is similar to that of the
interferometric modulator MEMS element described above. An
electrical potential between mechanical layer 814 and electrode 812
generates an electromotive force such that the mechanical layer 814
is attracted to electrode 812. When the potential, and therefore
attractive the electromotive force, is large enough, mechanical
layer 814 deflects towards electrode 812. Accordingly, the end of
mechanical layer 814 approaches terminal 810. When the deflection
of mechanical layer 814 is sufficient, mechanical layer 814
contacts terminal 810 and an electrical connection is established
between mechanical layer 814 and terminal 810.
After the electrical connection is established a signal driven onto
mechanical layer 814 will be transmitted to terminal 810.
Alternatively, after the electrical connection is established, a
signal driven onto terminal 810 will similarly be transmitted to
mechanical layer 814.
Once the electrical connection between mechanical layer 814 and
terminal 810 is no longer needed, the electric potential between
mechanical layer 814 and terminal 810 may be reduced until the
mechanical restorative force of mechanical layer 814 is greater
than the attractive electromotive force between mechanical layer
814 and terminal 810. In response to the greater restorative force,
the mechanical layer 814 returns towards a mechanically relaxed
position not contacting terminal 810. The electrical connection is
broken and the switch is again open and non-conductive.
Electrode 812 and terminal 810 may comprise one or more metallized
semiconductor materials such as, but not limited to, a metal
silicide, a metal germanide, and a metal germosilicide (e.g. NiSi,
CoSi.sub.2, MoSi, CoSi, TaSi, TiSi, and Ni(Si.sub.x-1Ge.sub.x)) in
different crystalline phases and compositions. Metallized
semiconductor materials comprise a metal and a semiconductor
material such as, but not limited to silicon, germanium, gallium
arsenide, Si.sub.x-1Ge.sub.x, alloys, and SiC. A benefit of
metallized semiconductors is shown in FIG. 8B, which illustrates
MEMS both element 818 of FIG. 8A and transistor 840 on substrate
820. Transistor 840 comprises gate electrode 837, gate oxide 835,
drain electrode 831, channel region 832, and source electrode 833.
Transistor 840 may be configured to directly or indirectly drive
MEMS element 818, or may be configured to directly or indirectly
sense a state of MEMS element 818. The material used for electrode
812 and/or terminal 810 may be similar to or substantially
identical to that used for drain electrode 831, channel region 832,
and source electrode 833. In some embodiments, electrode 812, drain
electrode 831, channel region 832, and source electrode 833 are
formed in substantially the same processing steps.
FIGS. 9A through 9D are cross-sections of the MEMS element 818 and
transistor 840 at various stages in a manufacturing process. The
following description is directed towards use of a semiconductor
material. Such semiconductor materials include materials which
comprise, for example, at least one of silicon, germanium, and
gallium arsenide. These and various other materials with
appropriate semiconductor and conductor properties may be used.
FIG. 9A shows substrate 920 and semiconductor layer 950 formed on
substrate 920. At this point in the manufacturing process,
semiconductor layer 950 may not substantially comprise metal. FIG.
9B shows semiconductor layer 950 after processing such that it is
formed into electrode semiconductor 902, terminal semiconductor
900, and transistor semiconductor 930. Transistor gate oxide 935
and transistor gate 937 are then formed over transistor
semiconductor 930, as shown in FIG. 9C. A metal is subsequently
deposited over substrate 920. The metal may comprise at least one
of nickel, molybdenum, cobalt, tantalum, and titanium. Other metals
may also be used. During a subsequent annealing process typically
at 300-900.degree. C., some of the deposited metal integrates into
the structure of the underlying electrode semiconductor 902,
terminal semiconductor 900, and transistor semiconductor 930. The
resulting material is advantageous for use both as a conductor,
such as electrode 912 and terminal 910, and as transistor
electrodes, such as gate electrode 937, drain electrode 933, and
source electrode 931, as shown in FIG. 9C. FIG. 9D shows insulator
908 and mechanical layer 914 fabricated by subsequent processing,
so as to complete MEMS element 918.
As indicated above, a portion of both a transistor and a MEMS
element may be substantially simultaneously fabricated. Because
metallized semiconductor materials are useful for both conductor
applications and transistor electrode and channel applications,
such simultaneous fabrication of different portions of a MEMS
device is especially advantageous, as these integrated devices can
be provided with reduced manufacturing complexity, size, and
cost.
Another characteristic of metallized semiconductors is that, in
addition to electrical and semiconductor properties, they have
optical reflectance properties which allow for advantageous use in
optical MEMS devices, such as interferometric modulator 1000, shown
in FIG. 10. While the following discussion is directed toward
interferometric modulator 1000, the aspects described herein are
not limited to this interferometric modulator embodiment, and can
be applied to any number of other interferometric modulator
embodiments, as well as any other optical MEMS device.
Interferometric modulator 1000 of FIG. 10 is similar in structure
and function to the interferometric modulators shown in FIGS.
7C-7E. Interferometric modulator 1000 comprises electrode 1016
formed on substrate 1020, insulator 1018 formed on electrode 1016,
and reflective layer 1014 supported by deformable mechanical layer
1134 formed above insulator 1018. Interferometric cavity 1010 is
formed between electrode 1016 and reflective layer 1014. As
described above, light .lamda. is introduced to interferometric
cavity 1010 through substrate 1020, electrode 1016, and insulator
1018. Light of color and intensity depending on interferometric
properties of interferometric cavity 1016 is reflected back through
insulator 1018, electrode 1016, and substrate 1020. Accordingly,
the optical properties and the electrical properties of electrode
1016 both affect the performance of interferometric modulator
1000.
Specifically, at least optical reflectance and electrical
resistivity are parameters affecting the performance of
interferometric modulator 1000. Electrode 1016 provides an
electrical function by serving as a conductor functioning to affect
the position of reflective layer 1014 so as to adjust a primary
dimension of interferometric cavity 1010, as described above. In
addition, electrode 1016 provides an optical function by serving as
a partially reflective layer, which defines a first major boundary
of interferometric cavity 1010, the other major boundary being
defined by the reflective layer 1014. In some interferometric
modulators, these two functions, electrical and optical, are
provided by two separate layers. For example, transparent ITO (or
other transparent conductive oxide, e.g. ZnO) may be used as the
conductor functioning to affect the position of the reflective
layer, and Cr may be used as a partially reflective layer, or
absorber, defining a first major boundary of the interferometric
cavity. However, in embodiments of this invention, a metallized
semiconductor layer is used to combine and perform the functions of
the ITO and Cr layers. Another benefit of using a metallized
semiconductor for the electrode/absorber is that the resistivity of
metallized semiconductor materials is lower than the resistivity of
ITO, as is shown in the following table:
TABLE-US-00001 RESISTIVITY OF VARIOUS MATERIALS Material
Resistivity (.mu..OMEGA.cm) ITO 120-500 Nickel silicide 20-60
Molybdenum silicide ~100 Cobalt silicide 18-25 Tantalum silicide
35-55 Titanium silicide 12-25
Accordingly, use of a metallized semiconductor allows for
production of thinner electrodes, while maintaining a desired low
resistance. For example NiSi can be used to form an electrode which
is from about 100 .ANG. to about 500 .ANG.. A MoSi electrode can be
from about 200 .ANG. to about 1000 .ANG.. A CoSi electrode can be
from about 50 .ANG. to about 200 .ANG., a TaSi electrode can be
from about 80 .ANG. to about 350 .ANG., and a TiSi electrode can be
from about 50 .ANG. to about 200 .ANG..
The electrical and optical properties of the single metallized
semiconductor layer can be tuned by the specific material used for
the metallized semiconductor layer and by the thickness of the
metallized semiconductor layer, its composition, crystalline phases
and dopants. For example, given two metallized semiconductor layers
of the same material and different thicknesses, the thicker layer
will have less electrical sheet resistance (.OMEGA./.quadrature.)
and greater optical reflectance in comparison to the thinner
layer.
Additionally, given two metallized semiconductor layers of the same
thickness and different materials, one will have greater optical
reflectance than the other and one will have greater electrical
sheet resistance (.OMEGA./.quadrature.) than the other, according
to the physical properties of the individual metallized
semiconductor materials. Accordingly, by intelligent selection of
material and thickness of the metallized semiconductor layer, the
electrical and optical properties can be tuned to desired values.
The following table shows resistivity (.mu..OMEGA.cm) of various
metallized semiconductor materials.
TABLE-US-00002 Resistivity Material (.mu..OMEGA.cm) TiSi.sub.2
13-16 ZrSi.sub.2 35-40 HfSi.sub.2 45-50 VSi.sub.2 50-55 NbSi.sub.2
50 TaSi.sub.2 35-45 CrSi.sub.2 ~600 MoSi.sub.2 ~100 WSi.sub.2 ~70
FeSi.sub.2 >1000 CoSi.sub.2 18-20 NiSi.sub.2 ~50 PtSi 600-800
Pd.sub.2Si 400
In addition, other processing parameters, such as, but not limited
to, doping concentration, annealing temperature, and annealing time
can be used to tune the electrical and optical properties of the
metallized semiconductor layer.
In addition to a single metallized semiconductor layer providing
both electrical and optical functions, an advantageous aspect of
using a metallized semiconductor layer for the electrode/absorber
is that semiconductor based electronic devices (e.g. transistors,
capacitors, memory devices, and microprocessors) can be
manufactured using some of the same processing steps as the
interferometric modulator integrated on the same substrate.
FIGS. 11A through 11C show a manufacturing process that can be used
to simultaneously manufacture a MEMS element 1100 and transistor
1140. FIGS. 11A through 11C are cross-sections of the
interferometric modulator 1000 and transistor 1140 at various
stages in a manufacturing process. The following description is
directed towards use of a semiconductor material. For example
materials which comprise at least one of silicon, germanium, and
gallium arsenide may be used. However, any material with
appropriate semiconductor and conductor properties may be used.
FIG. 11A shows substrate 1120 and semiconductor layer 1150 formed
on substrate 1120. At this point in the manufacturing process
semiconductor layer 1150 may not substantially comprise metal. FIG.
11B shows semiconductor layer 1150 after processing such that
semiconductor layer 1150 is formed into electrode semiconductor
1106 and transistor semiconductor 1130. Transistor gate oxide 1135
and transistor gate 1137 are subsequently formed over transistor
semiconductor 1130. A metal is subsequently deposited over
substrate 1120. The metal may comprise at least one of nickel,
molybdenum, cobalt, tantalum, and titanium. Other metals may also
be used. During a subsequent annealing process, some of the metal
integrates into the structure of the underlying electrode
semiconductor 1106 and transistor semiconductor 1130. The resulting
material is advantageous for use both as a conductor, such as
electrode 1116 and as transistor electrodes, such as gate electrode
1137, drain electrode 1133, and source electrode 1131, as is shown
in FIG. 11C. FIG. 11C also shows insulator 1118, reflective layer
1114, and mechanical layer 1134 fabricated by subsequent
processing, so as to complete interferometric modulator 1100.
As indicated, a portion of both a transistor and an interferometric
modulator may be substantially simultaneously fabricated. Because
metallized semiconductor materials are useful for optical
applications, conductor applications and transistor electrode
applications, such simultaneous fabrication of different portions
of an optical MEMS device is especially advantageous, as these
various applications can be provided with reduced manufacturing
complexity, cost and device size.
In order to implement the simultaneous processing of a transistor
and a MEMS element, such as those discussed above, the transistor
and the MEMS element may be may be manufactured or partially
manufactured on a thin film transistor (TFT) or semiconductor
production line.
TFT's are transistors in which the drain, source, and channel
region of the transistor are formed by depositing a semiconductor
over a base substrate. The semiconductor is appropriately patterned
so as to define the drain, source, and channel regions. Typically,
the base substrate is a non-semiconductor substrate. See, e.g.,
"Thin Film Transistors--Materials and Processes--Volume 1 Amorphous
Silicon Thin Film Transistors," ed. Yue Kuo, Kluwer Academic
Publishers, Boston (2004). The base substrate over which the TFT is
formed may be a non-semiconductor such as glass, plastic or metal.
The semiconductor that is deposited to form the channel region of
the TFT may, for example, comprise silicon (e.g., a-Si, a-SiH)
and/or germanium (e.g., a-Ge, a-GeH), and/or gallium arsenide
(e.g., a-GaAs), and may also comprise dopants such as phosphorous,
arsenic, antimony, and indium.
Certain MEMS devices may be at least partially processed on a TFT
production line simultaneously with certain TFT layers. For
example, the MEMS device shown in FIG. 8B, comprising MEMS element
818 and transistor 840, may be fabricated according to the process
described with reference to FIGS. 9A through 9D, where at least
some of the fabrication is performed on a TFT production line. For
example, the processing aspects described with reference to FIGS.
9A through 9C may occur on a TFT production line, while the
formation of insulator 908 and mechanical layer 914 may be
performed on a second production line. In some embodiments, the TFT
production line may be modified so as to be additionally capable of
performing these fabrication steps.
EXAMPLE 1
An interferometric modulator comprising ITO as an electrode and Cr
as an absorber and an interferometric modulator comprising NiSi as
a combined electrode/absorber were each simulated. Certain layers
and layer thicknesses and optical performance simulation results
are shown in the following table:
TABLE-US-00003 COMPARISON OF DESIGNS WITH Cr/ITO AND NiSi Cr/ITO
design NiSi design Layer Electrode 500 .ANG. (ITO) 200 .ANG. (NiSi)
Absorber 70 .ANG. (Cr) No layer needed Insulator 500 .ANG.
(Si0.sub.2)/80 .ANG. (Al.sub.2O.sub.3) 558 .ANG. (Si0.sub.2)/ 80
.ANG. (Al.sub.2O.sub.3) Cavity (Bright/Dark) 1550 .ANG./0 .ANG.
1255 .ANG./0 .ANG. Reflective Layer (Al) 300 .ANG. 300 .ANG.
Mechanical Layer 1000 .ANG. 1000 .ANG. Optical Performance: Y 52 70
CR 32 79 u' v' 0.155/0.468 0.171/0.470
FIGS. 12A and 12 show the reflectance of each of the simulated
interferometric modulators across wavelengths of visible light.
Comparing FIGS. 12A and 12B shows that the interferometric
modulator with the metallized semiconductor has better optical
performance at least because it has higher reflectance across
almost the entire band in the bright state, and has lower
reflectance across almost the entire band in the dark state.
While the above detailed description has shown, described, and
pointed out novel features as applied to various embodiments, it
will be understood that various omissions, substitutions, and
changes in the form and details of the device or process
illustrated may be made by those skilled in the art without
departing from the spirit of the invention. As will be recognized,
the present invention may be embodied within a form that does not
provide all of the features and benefits set forth herein, as some
features may be used or practiced separately from others.
* * * * *